Project Summary/Abstract - Project 2 (Kraus - PI) Interplay between the estrogen and progestin signaling pathways in the uterine myometrium during late gestation and at term drive the molecular events underlying the physiological processes leading to parturition. Defects in, or disruption of, these events can cause premature delivery or prolonged labor. Rising estrogen levels in late gestation act to prepare the myometrium for the events leading to parturition (e.g., increased myometrial contractility). However, the molecular details of estrogen action in the myometrium near term, including the mechanisms by which it antagonizes the maintenance of myometrial quiescence by progestins, are unclear. Estrogens (e.g., estradiol, E2) and progestins (e.g., progesterone, P4) act through steroid receptor proteins (estrogen receptors, ERs; progestin receptors, PR), which function as ligand-regulated DNA binding transcription factors. The activity of ER? is modulated through site-specific covalent post-translational modifications, including acetylation at lysines 266 and 268 (in human ER?), which increases both the DNA- binding and transcriptional activities of ER?. The long-term objectives of our proposed studies are to achieve a better understanding of key aspects of estrogen signaling in the myometrium near term and during parturition, namely: (1) the role of E2 signaling through ER?, (2) the molecular mechanisms by which E2-ER? antagonizes the progestational actions of P4- progestin receptor (PR) at the level of the genome, and (3) the molecular mechanisms by which ER? acetylation controls ER?-dependent gene regulation in the myometrium. Our hypotheses are that (1) the physiological actions of estrogens in the myometrium are determined by the repertoire of genomic binding sites (i.e., ?cistrome?) for ER?, as well as the target genes regulated by those ER? binding sites (enhancers), (2) increased estrogen signaling through ER? near term antagonizes P4 actions, in part, by altering the PR cistrome, and (3) acetylation regulates the ER? cistrome (e.g., formation, pattern, specificity, stability), ER? enhancer assembly, and the expression of target genes. In this proposal, we outline a series of experiments in three aims using an integrated approach with a complementary set of tools from biochemistry, molecular biology, genomics, mouse genetics, and physiology that will test our hypotheses. Collectively, our studies will reveal new aspects of the molecular mechanisms by which liganded ER? controls the biology of the myometrium during pregnancy and at term.